NFC: fix compiler warning about code never being executed when compiling on non windows platform.

llvm-svn: 348951
diff --git a/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp b/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
index bdb5436..62bd73f 100644
--- a/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
+++ b/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
@@ -78,12 +78,13 @@
 } // namespace
 
 static bool ShouldUseNativeReader() {
-#if !defined(_WIN32)
-  return true;
-#endif
+#if defined(_WIN32)
   llvm::StringRef use_native = ::getenv("LLDB_USE_NATIVE_PDB_READER");
   return use_native.equals_lower("on") || use_native.equals_lower("yes") ||
          use_native.equals_lower("1") || use_native.equals_lower("true");
+#else
+  return true;
+#endif
 }
 
 void SymbolFilePDB::Initialize() {